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<FONT color="green">001</FONT>    // Copyright 2005-08 Regents of the University of California.  May be used <a name="line.1"></a>
<FONT color="green">002</FONT>    // under the terms of the revised BSD license.  See LICENSING for details.<a name="line.2"></a>
<FONT color="green">003</FONT>    /** <a name="line.3"></a>
<FONT color="green">004</FONT>     * @author Adrian Mettler <a name="line.4"></a>
<FONT color="green">005</FONT>     */<a name="line.5"></a>
<FONT color="green">006</FONT>    package org.joe_e;<a name="line.6"></a>
<FONT color="green">007</FONT>    import org.joe_e.taming.Policy;<a name="line.7"></a>
<FONT color="green">008</FONT>    <a name="line.8"></a>
<FONT color="green">009</FONT>    /**<a name="line.9"></a>
<FONT color="green">010</FONT>     * Joe-E core library functions.  These provide fundamental features, similar<a name="line.10"></a>
<FONT color="green">011</FONT>     * to the methods in &lt;code&gt;java.lang.System&lt;/code&gt;, such as the interface to the<a name="line.11"></a>
<FONT color="green">012</FONT>     * overlay type system.<a name="line.12"></a>
<FONT color="green">013</FONT>     */<a name="line.13"></a>
<FONT color="green">014</FONT>    public class JoeE {<a name="line.14"></a>
<FONT color="green">015</FONT>        <a name="line.15"></a>
<FONT color="green">016</FONT>        private JoeE() {}<a name="line.16"></a>
<FONT color="green">017</FONT>    <a name="line.17"></a>
<FONT color="green">018</FONT>        /**<a name="line.18"></a>
<FONT color="green">019</FONT>         * Tests whether the specified object belongs to the specified type in the<a name="line.19"></a>
<FONT color="green">020</FONT>         * overlay type system. The equivalent of the Java &lt;code&gt;instanceof&lt;/code&gt;<a name="line.20"></a>
<FONT color="green">021</FONT>         * operator, for the overlay type system.  <a name="line.21"></a>
<FONT color="green">022</FONT>         * <a name="line.22"></a>
<FONT color="green">023</FONT>         * @param obj  the object to test<a name="line.23"></a>
<FONT color="green">024</FONT>         * @param type the type to test membership of<a name="line.24"></a>
<FONT color="green">025</FONT>         * @return true if the specified object belongs to the specified type<a name="line.25"></a>
<FONT color="green">026</FONT>         *  in the overlay type system.<a name="line.26"></a>
<FONT color="green">027</FONT>         */<a name="line.27"></a>
<FONT color="green">028</FONT>        static public boolean instanceOf(Object obj, Class&lt;?&gt; type) {<a name="line.28"></a>
<FONT color="green">029</FONT>            return obj != null &amp;&amp; isSubtypeOf(obj.getClass(), type);<a name="line.29"></a>
<FONT color="green">030</FONT>        }<a name="line.30"></a>
<FONT color="green">031</FONT>    <a name="line.31"></a>
<FONT color="green">032</FONT>        /**<a name="line.32"></a>
<FONT color="green">033</FONT>         * Tests whether the first class is a subtype of the second in the overlay<a name="line.33"></a>
<FONT color="green">034</FONT>         * type system.  <a name="line.34"></a>
<FONT color="green">035</FONT>         * <a name="line.35"></a>
<FONT color="green">036</FONT>         * @param c1 the potential subtype<a name="line.36"></a>
<FONT color="green">037</FONT>         * @param c2 the potential supertype<a name="line.37"></a>
<FONT color="green">038</FONT>         * @return true if the first argument is a subtype of the second in the<a name="line.38"></a>
<FONT color="green">039</FONT>         *  overlay type system<a name="line.39"></a>
<FONT color="green">040</FONT>         */<a name="line.40"></a>
<FONT color="green">041</FONT>        /*<a name="line.41"></a>
<FONT color="green">042</FONT>         * It might be hard to believe at first that an algorithm this simple<a name="line.42"></a>
<FONT color="green">043</FONT>         * can take into account all transitive dependencies correctly,<a name="line.43"></a>
<FONT color="green">044</FONT>         * but here is the key fact that makes it work:<a name="line.44"></a>
<FONT color="green">045</FONT>         * if C honorarily implements marker interface I, and D is a<a name="line.45"></a>
<FONT color="green">046</FONT>         * subclass of C, then either (1) D is from the Java library,<a name="line.46"></a>
<FONT color="green">047</FONT>         * in which case the honorary implementation guarantees that D<a name="line.47"></a>
<FONT color="green">048</FONT>         * will also be marked as honorarily implementing I; or (2) D is<a name="line.48"></a>
<FONT color="green">049</FONT>         * user code, in which case the Joe-E verifier requires D to explicitly<a name="line.49"></a>
<FONT color="green">050</FONT>         * implement I (in the Java type system).  In either case, this<a name="line.50"></a>
<FONT color="green">051</FONT>         * accounts for all transitive dependencies: in case (1), the call<a name="line.51"></a>
<FONT color="green">052</FONT>         * to honorarilyImplements() take care of transitive subtyping;<a name="line.52"></a>
<FONT color="green">053</FONT>         * in case (2), isAssignableFrom() takes care of it.<a name="line.53"></a>
<FONT color="green">054</FONT>         */<a name="line.54"></a>
<FONT color="green">055</FONT>        static public boolean isSubtypeOf(Class&lt;?&gt; c1, Class&lt;?&gt; c2) {<a name="line.55"></a>
<FONT color="green">056</FONT>            if (c2.isAssignableFrom(c1)) {<a name="line.56"></a>
<FONT color="green">057</FONT>                return true;<a name="line.57"></a>
<FONT color="green">058</FONT>            } else {<a name="line.58"></a>
<FONT color="green">059</FONT>                return Policy.hasHonorary(c1.getName(), c2.getName());<a name="line.59"></a>
<FONT color="green">060</FONT>            }<a name="line.60"></a>
<FONT color="green">061</FONT>        }<a name="line.61"></a>
<FONT color="green">062</FONT>        <a name="line.62"></a>
<FONT color="green">063</FONT>        /**<a name="line.63"></a>
<FONT color="green">064</FONT>         * This field holds the ErrorHandler to be invoked when <a name="line.64"></a>
<FONT color="green">065</FONT>         * &lt;code&gt;abort()&lt;/code&gt; is called.<a name="line.65"></a>
<FONT color="green">066</FONT>         * Trusted infrastructure (non-Joe-E) code may change the abort behavior <a name="line.66"></a>
<FONT color="green">067</FONT>         * by using unsafe reflection to modify the value of this field.<a name="line.67"></a>
<FONT color="green">068</FONT>         */<a name="line.68"></a>
<FONT color="green">069</FONT>        static private ErrorHandler handler = new SystemExit();<a name="line.69"></a>
<FONT color="green">070</FONT>        <a name="line.70"></a>
<FONT color="green">071</FONT>        /**<a name="line.71"></a>
<FONT color="green">072</FONT>         * Aborts the current flow of control.  This method invokes the currently<a name="line.72"></a>
<FONT color="green">073</FONT>         * registered error handler, which should preclude continued execution of <a name="line.73"></a>
<FONT color="green">074</FONT>         * Joe-E code.<a name="line.74"></a>
<FONT color="green">075</FONT>         * @param reason    reason for the abort<a name="line.75"></a>
<FONT color="green">076</FONT>         * @return an error to throw<a name="line.76"></a>
<FONT color="green">077</FONT>         */<a name="line.77"></a>
<FONT color="green">078</FONT>        static public Error abort(final Error reason) {<a name="line.78"></a>
<FONT color="green">079</FONT>            while (true) {<a name="line.79"></a>
<FONT color="green">080</FONT>                try {<a name="line.80"></a>
<FONT color="green">081</FONT>                    return handler.handle(reason);<a name="line.81"></a>
<FONT color="green">082</FONT>                } catch (final Throwable e) {<a name="line.82"></a>
<FONT color="green">083</FONT>                    // Keep trying...<a name="line.83"></a>
<FONT color="green">084</FONT>                }<a name="line.84"></a>
<FONT color="green">085</FONT>            }<a name="line.85"></a>
<FONT color="green">086</FONT>        }<a name="line.86"></a>
<FONT color="green">087</FONT>    <a name="line.87"></a>
<FONT color="green">088</FONT>        /**<a name="line.88"></a>
<FONT color="green">089</FONT>         * Is the object one-level deep immutable?<a name="line.89"></a>
<FONT color="green">090</FONT>         * @param x candidate object<a name="line.90"></a>
<FONT color="green">091</FONT>         * @return &lt;code&gt;true&lt;/code&gt; if &lt;code&gt;x&lt;/code&gt; is one-level deep immutable,<a name="line.91"></a>
<FONT color="green">092</FONT>         *         &lt;code&gt;false&lt;/code&gt; if it might not be<a name="line.92"></a>
<FONT color="green">093</FONT>         */<a name="line.93"></a>
<FONT color="green">094</FONT>        static public boolean<a name="line.94"></a>
<FONT color="green">095</FONT>        isFrozen(final Object x) {<a name="line.95"></a>
<FONT color="green">096</FONT>            return null == x ||<a name="line.96"></a>
<FONT color="green">097</FONT>                   instanceOf(x, Selfless.class) ||<a name="line.97"></a>
<FONT color="green">098</FONT>                   instanceOf(x, Immutable.class);<a name="line.98"></a>
<FONT color="green">099</FONT>        }<a name="line.99"></a>
<FONT color="green">100</FONT>    }<a name="line.100"></a>




























































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